Conventionally, there has been known a passive-driving type organic EL display device wherein an organic EL element having an organic luminous layer sandwiched between electrodes is driven by means of an XY matrix electrode structure. This type of organic EL display device is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2-37385 and 3-233891.
In such a passive-driving type organic EL display device, the so-called line-sequence driving is performed. Thus, in case that the device has several hundreds of scanning lines, required instantaneous brightness is several hundreds times larger than observed brightness. As a result, the following problems have been caused:                (1) Since the driving voltage becomes 2 to 3 times higher than a regular DC voltage, the luminous efficiency is lowered or the power consumption becomes large.        (2) Since the electric current instantaneously becomes several hundreds times larger, the organic luminous layer tends to deteriorate.        (3) Since the amount of electric current is very large in the same way as in the item (2), a voltage drop in the wiring of electrodes becomes large.        
Therefore, in order to solve the problems that the passive-driving type organic EL display device has, there have been suggested an active-driving type organic EL display device having thin film transistors (which may be referred to as TFTs, hereinafter) to drive organic EL elements.
Such an active-driving type organic EL display device has features of its driving voltage being drastically lowered, the luminous efficiency thereof is improved, and of its power consumption being reduced, or the like, as compared with the passive-driving type organic EL display device.
However, even the active-driving type organic EL display device having such effects as above has a problem that the reliability of connection between its organic EL elements and TFTs is poor. For example, it is suggested that the organic EL elements and TFTs be electrically connected by using a metal material such as aluminum or chromium. However, a transparent electrode, for example ITO (indium tin oxide), of the organic EL elements, thereof has easily stripped from those metal materials. The metal material has corroded because of water content present in the surroundings. What is worse, the migration has occurred, causing a leakage current.
As shown in FIG. 19, JP-A Nos. 8-330600 and 10-254383 disclose an organic EL display device 200 having an organic EL element 226 and a TFT 237, as well as having an electrically connecting member 228 made of a composite material for electrically connecting the EL element 226 to the TFT 237.
In this organic EL display device 200, a composite thin film composed of a metal thin film made of a low-resistance material for a lower layer 250, and a titanium nitride thin film having superior corrosion-resistance for an upper layer 251, is disclosed for the electrically connecting member. For example, a barrier metal made of aluminum/titanium nitride, tungsten/titanium nitride, molybdenum/titanium nitride, or the like is used for the composite thin film.
As shown in FIG. 20, JP-A No. 10-189252 discloses an active-driving type organic EL display device 300 wherein a drain region 347 of a TFT 344 is electrically connected to a lower electrode 302 of an organic EL element 326 are through a contact hole (via hole) 354 which is vertically formed in an inter-insulator 313.
However, in the active-driving type organic EL display device 200 disclosed in the aforementioned JP-A No. 8-330600 and 10-254383, the barrier metal composed of the metal thin film of the lower layer 250 and the titanium nitride thin film of the upper layer 251 is horizontally formed to connect a drain region 236 of the TFT 237 to a lower electrode 222 of the organic EL element electrically. Therefore, if a color-converting medium (not shown) such as a thick color filter or color-converting film is provided adjacent the lower electrode of the organic EL element 226 for example, the following problems arise: (i) A level-difference between the drain region of the TFT and the lower electrode is generated to make it difficult to connect them electrically to each other; (ii) The barrier metal is easily damaged so that the reliability of the connection becomes poor or the like. Although the color-converting medium was made thin, a new problem that the color-converting efficiency is lower has been encountered.
If the color-converting medium (not shown) provided adjacent the lower electrode of the active-driving type organic EL display device 300 disclosed in the aforementioned JP-A No. 10-189252 is made thick, the reliability may be lowered for the electric connection through the vertically-formed contact hole 354.
That is to say, if the thickness of the color-converting medium is made, for example, 5 μm or more thick, the thermal expansion of the color-converting medium becomes large when the medium is heated, thereby the wires snapping in the contact hole having a thermal expansion smaller than that of the color-converting medium.
According to the electric connection using the vertically-formed contact hole 354, it is difficult that an electro-conductive material is uniformly filled into the contact hole since this hole is long. It has been substantially impossible to use a vapor-deposition method or a sputtering method, which is an ordinary method for forming an electrically connecting member.
Thus, the present inventors have made eager investigations on the above-described problems, thereby finding out that by disposing an electrically connecting member obliquely between an organic EL element and a TFT, superior connection reliability can be obtained with the above-described problems being solved.
That is, an object of the present invention is to provide an active-driving type organic EL display device wherein a lower electrode of an organic EL element can easily be connected electrically to a drain region of a TFT even if a color-converting medium having a thickness of, for example, 5 μm or more is provided adjacent the lower electrode, so that superior connection reliability can be obtained.
Another object of the present invention is to provide a producing method making it possible to supply such an active-driving type organic EL display device efficiently.